Method and apparatus for device-to-device user equipment to transmit discovery signal in wireless communication system

ABSTRACT

One embodiment of the present invention relates to a method for a device-to-device (D2D) user equipment to transmit a discovery signal in a wireless communication system, the method comprising the steps of: choosing a resource pool from among one or more resource pools; and transmitting a discovery signal by using the resources of the chosen resource pool, wherein the resource pool is chosen on the basis of RSRP measurement results.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2015/002347, filed on Mar. 11, 2015, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application Nos. 61/950,842filed on Mar. 11, 2014, 61/994,109 filed on May 15, 2014, 62/031,155filed on Jul. 30, 2014, and 62/033,639 filed on Aug. 5, 2014, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system and,more particularly, to a method and apparatus for transmitting adiscovery signal through device-to-device communication.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmit power, etc.) among them. Forexample, multiple access systems include a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system, and a Multi-Carrier FrequencyDivision Multiple Access (MC-FDMA) system.

D2D communication is a communication scheme in which a direct link isestablished between User Equipments (UEs) and the UEs exchange voice anddata directly with each other without intervention of an evolved Node B(eNB). D2D communication may cover UE-to-UE communication andpeer-to-peer communication. In addition, D2D communication may find itsapplications in Machine-to-Machine (M2M) communication and Machine TypeCommunication (MTC).

D2D communication is under consideration as a solution to the overheadof an eNB caused by rapidly increasing data traffic. For example, sincedevices exchange data directly with each other without intervention ofan eNB by D2D communication, compared to legacy wireless communication,the overhead of a network may be reduced. Further, it is expected thatthe introduction of D2D communication will reduce the power consumptionof devices participating in D2D communication, increase datatransmission rates, increase the accommodation capability of a network,distribute load, and extend cell coverage.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method for transmitting a signal in consideration of interferencebetween the WAN signal transmission and D2D signal transmission.

The technical objects that can be achieved through the present inventionare not limited to the aforementioned technical object and othertechnical which are not mentioned herein will be clearly understood bypersons skilled in the art from the following detailed description.

Technical Solution

The object of the present invention can be achieved by providing amethod for transmitting a discovery signal by a Device-to-Device (D2D)terminal in a wireless communication system, the method includingselecting a resource pool from among one or more resource pools, andtransmitting a discovery signal using resources of the selected resourcepool, wherein the resource pool is selected according to an RSRPmeasurement result.

In another aspect of the present invention, provided herein is aDevice-to-Device (D2D) terminal for transmitting a discovery signal in awireless communication system, the D2D terminal including a receptionmodule, and a processor, wherein the processor is configured to select aresource pool from among one or more resource pools and to transmit adiscovery signal using resources of the selected resource pool, whereinthe resource pool is selected according to an RSRP measurement result.

The aspects of the present invention may include some or all of thefollowing details.

An RSRP range may be configured for each of the one or more resourcepools.

Open loop power control may be applied to the transmitting of thediscovery signal.

P₀ and α used in determining a transmit power of the discovery signalmay be delivered through a higher layer signaling, wherein P₀ may denotea minimum transmit power, and α may denote a path loss coefficient.

Possible values of α may include 0.

A transmit power of the discovery signal may be determined by thefollowing equation:

${{P_{D\; 2D\text{-}{Discovery}}(i)} = {\min\begin{Bmatrix}{{{P_{CMAX}(i)},}\mspace{355mu}} \\{P_{0_{—}D\; 2D_{—}{Discovery}} + {\alpha \cdot {PL}} + \Delta_{D\; 2D_{—}{Discovery}}}\end{Bmatrix}}},$wherein P_(0_D2D_Discovery) may denote a minimum transmit power, PL maydenote a path loss, Δ_(D2D_Discovery) may denote a power boostingparameter, and α may denote a path loss coefficient.

A size of a resource unit for transmitting the discovery signal may varyaccording to the RSRP measurement result.

When the D2D terminal is an out-of-coverage terminal, the size of theresource unit for transmitting the discovery signal may be preset by anetwork operator.

A given number of times of repetition of the discovery signal may beallocated to each of the one or more resource pools.

The number of times of repetition may be determined according to a sizeof the resource pool in the frequency domain.

A transmit power used in transmitting a physical uplink control channelin a subframe used to transmit the discovery signal may be greater thana transmit power used in transmitting the physical uplink controlchannel in a subframe unused to transmit the discovery signal.

A parameter related to the transmit power used in transmitting thephysical uplink control channel in the subframe used to transmit thediscovery signal may be delivered through higher layer signaling.

Advantageous Effects

According to embodiments of the present invention, a discovery signalmay be transmitted with minimized influence of interference on PUCCHtransmission.

It will be appreciated by those skilled in the art that the effects thatcan be achieved with the present invention are not limited to what hasbeen described above and other advantages of the present invention willbe clearly understood from the following detailed description taken inconjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates a radio frame structure.

FIG. 2 is a diagram illustrating a resource grid for a downlink slot.

FIG. 3 illustrates the structure of a downlink subframe.

FIG. 4 illustrates the structure of an uplink subframe.

FIGS. 5 to 7 illustrate resource selection for transmitting a discoverysignal according to an embodiment of the present invention.

FIG. 8 is a diagram illustrating configuration of transceivers.

BEST MODE

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions or features ofany one embodiment may be included in another embodiment and may bereplaced with corresponding constructions or features of anotherembodiment.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aBase Station (BS) and a User Equipment (UE). The BS is a terminal nodeof a network, which communicates directly with a UE. In some cases, aspecific operation described as performed by the BS may be performed byan upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point(AP)’, etc. The term ‘relay’ may be replaced with the term ‘Relay Node(RN)’ or ‘Relay Station (RS)’. The term ‘terminal’ may be replaced withthe term ‘LIE’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station(MSS)’, ‘Subscriber Station (SS)’, etc. In addition, in the followingembodiments, the term “base station” may mean an apparatus such as ascheduling node or a cluster header. If the base station or the relaytransmits a signal transmitted by a terminal, the base station or therelay may be regarded as a terminal.

The term “cell” may be understood as a base station (BS or eNB), asector, a Remote Radio Head (RRH), a relay, etc. and may be acomprehensive term referring to any object capable of identifying acomponent carrier (CC) at a specific transmission/reception (Tx/Rx)point.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed for at least one of wireless access systems,Institute of Electrical and Electronics Engineers (IEEE) 802, 3rdGeneration Partnership Project (3GPP), 3GPP Long Term Evolution (3GPPLTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are notdescribed to clarify the technical features of the present invention canbe supported by those documents. Further, all terms as set forth hereincan be explained by the standard documents.

Techniques described herein can be used in various wireless accesssystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier-FrequencyDivision Multiple Access (SC-FDMA), etc. CDMA may be implemented as aradio technology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications (GSM)/General Packet Radio Service(GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may beimplemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a partof Universal Mobile Telecommunications System (UMTS). 3GPP LTE is a partof Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LIE employs OFDMA fordownlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.WiMAX can be described by the IEEE 802.16e standard (WirelessMetropolitan Area Network (WirelessMAN)-OFDMA Reference System) and theIEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity,this application focuses on the 3GPP LIE and LTE-A systems. However, thetechnical features of the present invention are not limited thereto.

LTE/LTE-A Resource Structure/Channel

With reference to FIG. 1, the structure of a radio frame will bedescribed below.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) wirelesspacket communication system, uplink and/or downlink data packets aretransmitted in subframes. One subframe is defined as a predeterminedtime period including a plurality of OFDM symbols. The 3GPP LTE standardsupports a type-1 radio frame structure applicable to Frequency DivisionDuplex (FDD) and a type-2 radio frame structure applicable to TimeDivision Duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into 10 subframes. Each subframe is further dividedinto two slots in the time domain. A unit time during which one subframeis transmitted is defined as a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms in duration and one slot may be 0.5 msin duration. A slot includes a plurality of OFDM symbols in the timedomain and a plurality of Resource Blocks (RBs) in the frequency domain.Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbolrepresents one symbol period. An OFDM symbol may be referred to as anSC-FDMA symbol or symbol period. An RB is a resource allocation unitincluding a plurality of contiguous subcarriers in a slot.

The number of OFDM symbols in one slot may vary depending on a CyclicPrefix (CP) configuration. There are two types of CPs: extended CP andnormal CP. In the case of the normal CP, one slot includes 7 OFDMsymbols. In the case of the extended CP, the length of one OFDM symbolis increased and thus the number of OFDM symbols in a slot is smallerthan in the case of the normal CP. Thus, when the extended CP is used,for example, 6 OFDM symbols may be included in one slot. If channelstate gets pool, for example, during fast movement of a UE, the extendedCP may be used to further decrease Inter-Symbol Interference (ISI).

In the case of the normal CP, one subframe includes 14 OFDM symbolsbecause one slot includes 7 OFDM symbols. The first two or three OFDMsymbols of each subframe may be allocated to a Physical Downlink ControlCHannel (PDCCH) and the other OFDM symbols may be allocated to aPhysical Downlink Shared Channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. A type-2 radioframe includes two half frames, each having 5 subframes, a DownlinkPilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot TimeSlot (UpPTS). Each subframe is divided into two slots. The DwPTS is usedfor initial cell search, synchronization, or channel estimation at a UE.The UpPTS is used for channel estimation and acquisition of uplinktransmission synchronization to a UE at an eNB. The GP is a periodbetween an uplink and a downlink, which eliminates uplink interferencecaused by multipath delay of a downlink signal. One subframe includestwo slots irrespective of the type of a radio frame.

The above-described radio frame structures are purely exemplary and thusit is to be noted that the number of subframes in a radio frame, thenumber of slots in a subframe, or the number of symbols in a slot mayvary.

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot. A downlink slot includes 7 OFDM symbolsin the time domain and an RB includes 12 subcarriers in the frequencydomain, which does not limit the scope and spirit of the presentinvention. For example, a downlink slot may include 7 OFDM symbols inthe case of the normal CP, whereas a downlink slot may include 6 OFDMsymbols in the case of the extended CP. Each element of the resourcegrid is referred to as a Resource Element (RE). An RB includes 12×7 REs.The number of RBs in a downlink slot, NDL depends on a downlinktransmission bandwidth. An uplink slot may have the same structure as adownlink slot.

FIG. 3 illustrates the structure of a downlink subframe. Up to threeOFDM symbols at the start of the first slot in a downlink subframe areused for a control region to which control channels are allocated andthe other OFDM symbols of the downlink subframe are used for a dataregion to which a PDSCH is allocated. Downlink control channels used inthe 3GPP LTE system include a Physical Control Format Indicator CHannel(PCFICH), a Physical Downlink Control CHannel (PDCCH), and a PhysicalHybrid automatic repeat request (HARQ) Indicator CHannel (PHICH). ThePCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH delivers an HARQACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled Downlink Control Information (DCI). The DCI transports uplink ordownlink scheduling information, or uplink transmit power controlcommands for UE groups. The PDCCH delivers information about resourceallocation and a transport format for a Downlink Shared CHannel(DL-SCH), resource allocation information about an Uplink Shared CHannel(UL-SCH), paging information of a Paging CHannel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a Random Access Responsetransmitted on the PDSCH, a set of transmit power control commands forindividual UEs of a UE group, transmit power control information, VoiceOver Internet Protocol (VoIP) activation information, etc. A pluralityof PDCCHs may be transmitted in the control region. A UE may monitor aplurality of PDCCHs. A PDCCH is formed by aggregating one or moreconsecutive Control Channel Elements (CCEs). A CCE is a logicalallocation unit used to provide a PDCCH at a coding rate based on thestate of a radio channel. A CCE includes a plurality of RE groups. Theformat of a PDCCH and the number of available bits for the PDCCH aredetermined according to the correlation between the number of CCEs and acoding rate provided by the CCEs. An eNB determines the PDCCH formataccording to DCI transmitted to a UE and adds a Cyclic Redundancy Check(CRC) to control information. The CRC is masked by an Identifier (ID)known as a Radio Network Temporary Identifier (RNTI) according to theowner or usage of the PDCCH. If the PDCCH is directed to a specific UE,its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If the PDCCH isfor a paging message, the CRC of the PDCCH may be masked by a PagingIndicator Identifier (P-RNTI). If the PDCCH carries system information,particularly, a System Information Block (SIB), its CRC may be masked bya system information ID and a System Information RNTI (SI-RNTI). Toindicate that the PDCCH carries a Random Access Response in response toa Random Access Preamble transmitted by a UE, its CRC may be masked by aRandom Access-RNTI (RA-RNTI).

FIG. 4 illustrates the structure of an uplink subframe. An uplinksubframe may be divided into a control region and a data region in thefrequency domain. A Physical Uplink Control CHannel (PUCCH) carryinguplink control information is allocated to the control region and aPhysical Uplink Shared Channel (PUSCH) carrying user data is allocatedto the data region. To maintain the property of a single carrier, a UEdoes not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UEis allocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Uplink Power Control

Uplink power control is applied to the LTE/LTE-A system such that theLTE/LTE-A system may easily demodulate uplink control information, data,etc. The uplink power control may be classified into PUCCH powercontrol, PUSCH power control, and UL Sounding Reference Signal (SRS)power control.

The PUCCH power control is determined considering path loss, maximumtransmit power of the UE, and the like, such that control informationtransmitted on the PUCCH may be demodulated at a sufficiently low errorrate.

Specifically, the PUCCH power control in subframe i of cell ‘c’ may beimplemented according to Equation 1 below.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min{\begin{Bmatrix}{{{P_{{CMAX},c}(i)},}\mspace{680mu}} \\{P_{0_{—}{PUCCH}} + {PL}_{c} + {h\left( {n_{CQI},n_{HARQ},n_{SR}} \right)} + {\Delta_{F_{—}{PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g(i)}}\end{Bmatrix}\mspace{11mu}\lbrack{dBm}\rbrack}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Herein, P_(CMAX,c)(i) denotes a maximum transmit power of the UE, andserves as the upper limit of the PUCCH power control command.

P_(0_PUCCH) is a PUCCH transmit power value that the eNB desires toreceive. This value is transmitted through higher layer signaling as aUE-specific parameter, and is determined to be the sum of nominal powervalues P_(O_NOMINAL_PUCCH) and P_(O_UE_PUCCH).

PL_(c) is a path loss value in cell c, which is estimated by the UE.This value may be estimated by the UE by measuring the receive power ofa DL cell-specific reference signal (CRS).

h(n_(CQI),n_(HARQ),n_(SR)) is a value dependent upon a PUCCH format,n_(CQI) is the number of bits indicating channel quality information,n_(HARQ) is the number of HARQ bits, and n_(SR) is set to 1 if thesubframe i is set for request for scheduling and is set to 0 otherwise.h(n_(CQI),n_(HARQ),n_(SR)) is dependent upon the PUCCH format.Specifically, i) h(n_(CQI),n_(HARQ),n_(SR)) is set to 0 in the case ofPUCCH formats 1, 1a, and 1b, ii) h(n_(CQI),n_(HARQ),n_(SR)) is set to

$\frac{\left( {n_{HARQ} - 1} \right)}{2}$if one or more serving cells are used in PUCCH format 1b, and iii)h(n_(CQI),n_(HARQ),n_(SR)) is set to

$10{\log_{10}\left( \frac{n_{CQI}}{4} \right)}$if normal cyclic prefix (CP) is used in PUCCH formats 2, 2a and 2b.

Δ_(F_PUCCH)(F) is signaled from a higher layer in consideration of MCS.Δ_(F_PUCCH)(F) indicates necessity of different signal-to-noiseinterference ratios (SINR) in response to not only the number of bitsper subframe of the PUCCH format but also different error rates.

Δ_(TxD)(F′) is a power offset signaled from a higher layer when thePUCCH is transmitted using two antenna ports, and is dependent upon thePUCCH format.

g(i) is an accumulation value of the current PUCCH power controladjustment states, and is determined by a power value δ_(PUCCH)corresponding to the value of a transmit power control (TPC) commandfield included in a DCI format transmitted over a PDCCH and a PUCCHpower control adjustment state value g(i−1) of a previous subframe.

Subsequently, PUSCH power control in the case where PUCCH transmissionis not performed may be determined by Equation 2.

$\begin{matrix}{{P_{{PUSCH},c}(i)} = {\min{\begin{Bmatrix}{{{P_{{CMAX},c}(i)},}\mspace{616mu}} \\{{10{\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O_{—}{PUSCH}},c}(j)} + {{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} + {f_{c}(i)}}\end{Bmatrix}\mspace{14mu}\lbrack{dBm}\rbrack}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

P_(CMAX,c)(i) denotes a maximum transmit power of the UE, andM_(PUSCH, c) (i) denotes a PUSCH transmission bandwidth represented bythe number of RBs.

P_(O_PUSCH,c)(j) denotes a PUSCH transmit power value that the eNBdesires to receive. This value is determined to be the sum of nominalpower values P_(O_NOMINAL_PUCCH) and P_(O_UE_PUCCH). For semi-persistentscheduling, j is set to 0 (j=0). For dynamic scheduling, j is set to 1(j=1). For a random access response, j is set to 2 (j=2).

α_(c)(j)·PL_(c) is a downlink path loss, where PL_(c) is estimated bythe UE, and α_(c)(j) is a path loss compensation value transmittedthrough higher layer signaling. If j=0 or j=1, α_(c)∈{0, 0.4, 0.5, 0.6,0.7, 0.8, 0.9, 1} is obtained. If j=1, α_(c)(j)₌₁.

Δ_(TF,c)(i) is calculated using a value transmitted through higher layersignaling, BPRE (Bit Per Resource Element), CQI, PMI, etc.

f_(c)(i) is an accumulated value and is determined by a power valueδ_(PUSCH) corresponding to a TPC (transmit power control) command fieldvalue included in a DCI format transmitted on PDCCH, the value ofK_(PUSCH), which depend upon configuration such as FDD, TDD, or thelike, and an accumulated value f_(c)(i−1) obtained through accumulationup to the previous subframe.

If PUCCH transmission is performed along with PUSCH transmission, thePUSCH power control is expressed by Equation 3 below.

$\begin{matrix}{{P_{{PUSCH},c}(i)} = {\min{\begin{Bmatrix}{10{\log_{10}\left( {{{{\hat{P}}_{{CMAX},c}(i)} - {{\hat{P}}_{PUCCH}(i)}},}\mspace{385mu} \right.}} \\{{10{\log_{10}\left( {M_{{PUSCH},c}(i)} \right)}} + {P_{{O_{—}{PUSCH}},c}(j)} + {{\alpha_{c}(j)} \cdot {PL}_{c}} + {\Delta_{{TF},c}(i)} + {f_{c}(i)}}\end{Bmatrix}\mspace{14mu}\lbrack{dBm}\rbrack}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

{circumflex over (P)}_(CMAX,c)(i) has a linear value with respect toP_(CMAX,c)(i), and {circumflex over (P)}_(PUCCH)(i) is a linear valuefor PUCCH power control determined by Equation 3. The remainingparameters have meanings as disclosed above.

Acquisition of Synchronization between D2D UEs

Hereinafter, description will be given of acquisition of synchronizationbetween UEs in D2D communication based on the above description and thelegacy LTE/LTE-A system. If time/frequency synchronization is notobtained in the OFDM system, OFDM signals may not be multiplexed betweendifferent UEs due to inter-cell interference. It is inefficient for allD2D UEs to individually match synchronization by directly transmittingand receiving a synchronization signal. Accordingly, in a distributednode system such as the D2D system, a specific node may transmit arepresentative synchronization signal, and the other UEs may matchsynchronization therewith. In other words, to perform transmission andreception of a D2D signal, some nodes (which may be referred to as eNBs,UEs, SRNs (synchronization reference nodes) or synchronization sources)may transmit a D2D synchronization signal (D2DSS), and the other UEs maytransmit or receive a signal in synchronization therewith.

The D2DSSs may include a primary D2DSS (PD2DSS) and a secondary D2DSS(SD2DSS). The PD2DSS may have a similar/modified/repeated structure of aZadoff-Chu sequence having a predetermined length or a PSS. The SD2DSSmay have a similar/modified/repeated structure of an M-sequence or anSSS. When UEs are synchronized with an eNB, the eNB serves as an SRN,the PSS/SSS serves as a D2DSS. The physical D2D synchronization channel(PD2DSCH) may be a (broadcast) channel on which basic (system)information (e.g., information related to the D2DSS, the duplex mode(DM), TDD UL/DL configuration, resource pool-related information, thetype of an application related to the D2DSS, etc.) which a UE needs tocheck before transmitting and receiving a D2D signal is transmitted. ThePD2DSCH may be transmitted in the subframe in which the D2DSS istransmitted or in a subsequent subframe.

The SRN may be a node to transmit the D2DSS and physical D2Dsynchronization channel (PD2DSCH). The D2DSS may take the form of aspecific sequence, and the PD2DSCH may take the form of a sequencerepresenting specific information or a codeword obtained throughpredetermined channel coding. Herein, the SRN may be an eNB or aspecific D2D UE. When the UE is within a partial network coverage or outof network coverage, the UE may serve as an SRN. In the case ofinter-cell discovery, the UE may relay a D2DSS a certain offset afterthe timing of reception of the D2DSS from the SRN in order to makeinter-cell UEs recognize timing. That is, The D2DSS may be relayedthrough multiple hops. If multiple UEs relay the D2DSS or there aremultiple clusters around the UE, the UE to receive a D2DSS may observemultiple D2DSSs and receive D2DSSs having different hops.

Discovery Signal Transmission and PUCCH Transmission

In D2D communication, discovery signal transmission for discoverybetween UEs may be divided into the following two types. Type 1discovery signal transmission is discovery signal transmission performedwhen allocation of discovery signal transmission resources is notUE-specific, and type 2 discovery signal transmission is signaltransmission performed when allocation of discovery signal transmissionresources is UE-specific. In type 1 discovery signal transmission, thenetwork may configure only the resource region in which a discoverysignal is transmitted, and the UE may determine resources in theresource region (based on any, random or energy sensing) to transmit thediscovery signal. Herein, the resource region in which the discoverysignal is transmitted may not overlap the PUCCH resource region. Morespecifically, PUCCH resources may be excluded from the resource regionfor discovery signal transmission because the PUCCH resources are usedby legacy UEs to transmit ACK/NACK or CSI. In addition, power controlmay be applied to PUCCH transmission. Accordingly, in performingdiscovery signal transmission, PUCCH transmission may undergo severeinterference due to, for example, inband emission. In this regard,methods to protect both discovery signal transmission and PUCCHtransmission will be discussed below. In the following disclosure, arelationship between discovery signal transmission and PUCCHtransmission will be mainly described, but it should be noted that thepresent invention is not limited thereto. The present invention is alsoapplicable to a relationship between transmission of a D2D signaldifferent from the discovery signal and transmission of a WAN signal.

Open Loop Power Control

In performing discovery signal transmission, PUCCH transmission may beprotected through transmit power control. Herein, the transmit powercontrol which is suitable for the operation in terms of nature ofdiscovery signal transmission would be open loop power control (Closedloop power control may be adopted depending on the D2D signal type).That is, when the UE transmits a discovery signal, the transmit powermay be given by Equation 4 below.

$\begin{matrix}{{P_{D\; 2D\text{-}{Discovery}}(i)} = {\min\begin{Bmatrix}{{{P_{CMAX}(i)},}\mspace{355mu}} \\{P_{0_{—}D\; 2D_{—}{Discovery}} + {\alpha \cdot {PL}} + \Delta_{D\; 2D_{—}{Discovery}}}\end{Bmatrix}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

In this equation, P_(0_D2D_Discovery) denotes the minimum transmitpower, PL denotes path loss, Δ_(D2D_Discovery) is a power boostingparameter (power offset, power offset parameter), and α is a path losscoefficient (0=<α=<1, where α is 1 for PUCCH). Herein,P_(0_D2D_Discovery), α and Δ_(D2D_Discovery) may have valuespre-signaled to the UE or preset/preconfigured values. That is,P_(0_D2D_Discovery) and α may be signaled to the UE through higher layersignaling (e.g., RRC signaling), broadcasting or physical layersignaling (system information block, PDCCH, EPDCCH, or the like).Parameters related to the power control may also be signaled using themethod described above. The backoff parameter Δ_(D2D_Discovery) is anoffset introduced to transmit a D2D signal at a lower (or higher) powerin case that P_(0_D2D_Discovery) reuses the value of another cellularchannel. The maximum D2D transmit power may be set to a value separatefrom existing P_(CMAX).

Parameters which are not signaled among the aforementioned parametersmay be preset to specific values, reuse the values signaled for cellularuse, or have values which are delivered through separate signaling forD2D during reuse of the values signaled for cellular use. For example,P_(0_D2D_Discovery) and α may be set to the values of the legacy PUSCHor PUCCH and thus may not be separately signaled. Instead,Δ_(D2D_Discovery) may be signaled for D2D.

Adjustment of the power for discovery signal transmission may beimplemented as stepwise transmit power adjustment. For example, if thesignal strength (RSRP, RSRQ) from the eNB is lower than or equal to apreset threshold, the signal may be transmitted at a preset transmitpower X dBm. If the signal strength is greater than the threshold, thesignal may be transmitted at Y dBm. Y may be set to be less than X. Suchstepwise transmit power setting is not limited to the 2 steps. Thetransmit power setting may be generalized as setting M transmit powervalues. In this case, the threshold for the signal strength from the eNBand the transmit power within the threshold range may have preset valuesor be signaled from the eNB to the UE through a physical layer signal orhigher layer signal.

Determination of Transmission Resources According to Signal Intensityfrom the eNB

The region for transmission of a discovery signal may be separatelyconfigured according to the signal strength of the eNB (which may beRSRP, RSRQ or a value related to the strength the received signal fromthe eNB). Specifically, one or more resource pools for transmission ofdiscovery signals may be configured, and the range of RSRP (or a valuerelated to the received signal strength such as RSRQ) may be configuredfor each of the resource pools. Thereby, a specific D2D UE may select aresource pool in the range including RSRP, and transmit a discoverysignal using a resource for discovery signal transmission in theresource pool (wherein the resource may be randomly selected in theresource pool). That is, a UE having type 1 discovery configuredtherefor may select a resource pool from among one or more resourcepools, and transmit the discovery signal using a resource in theselected resource pool. Herein, the resource pool is selected based onthe RSRP measurement result. Examples of this operation are illustratedin FIGS. 5 and 6. Referring to FIG. 5, two resource pools are configuredfor a discovery signal. And an RSRP range is configured for each of thetwo resource pools. For example, resource pool 1 may be for an RSRPrange between −110 and −80, and resource pool 2 may be for an RSRP rangebetween −80 and −60. UEs (e.g., UEs belonging to UE growth #1) which areat similar distances from the eNB and have RSRPs similar to each othermay transmit discovery signals using resources in the same resourcepool. While FIG. 5 illustrates configuring resource pools according to aTDM scheme, multiple resource pools may be configured according to FDMas illustrated in FIG. 6 or a combination of TDM and FDM, which is notshown.

Such configuration may allow UEs having the same repetition factor (orthe same unit size) to perform transmission in similar resource regions,thereby simplifying design of a hopping pattern. In addition, thisconfiguration allows UEs close to each other or having similar transitpowers to perform transmission (simultaneously) on the same resource inconsideration of inband emission, thereby attenuating degradation ofperformance caused by inband emission. For example, when two UEs are faraway from each other, it may be impossible for the receiving UE toreceive a signal from the UE which is far away therefrom due to inbandemission of a specific UE close thereto. In this case, the UEs may beconfigured to perform transmission simultaneously, thereby alleviatingthe above phenomenon.

The operation of distinguishing between resource pools according to theRSRP may be extended to distinguish transmission resource regionsaccording to the magnitude of the transmit power regardless of the RSRP.For example, if UEs of a specific group transmit (are capable oftransmitting) discovery signals at a high transmit power, the timeresource region of the UEs of the specific group may be configured to bedifferent from that of a UE having low transmit power. The discoverysignal transmission resource region (resource pool) according to thesignal strength (or transmit power) of the eNB may be pre-configured ordelivered by the network through physical layer signaling (SIB,PDCCH/EPDCCH, etc.) or higher layer signaling (RRC signaling). Forexample, the network may deliver configuration of multiple resourcepools and the transmit power for each of the resource pools to the UEthrough physical layer signaling or higher layer signaling. The UE mayselect a resource pool according to a target discovery range (a targetcommunication range for communication signals), and transmit a discoverysignal at the transmit power which is set for the selected resourcepool.

As described above, selection of a resource pool according to the RSRPor transmit power may be used together with embodiments which will bedescribed below. For example, transmission may be performed at transmitpower P_A dBm N_A times in resource pool A, and may be performed attransmit power P_B dBm N_B times in resource pool B. in this case, thenumber of times of repetition in each resource pool may be signaled bythe network through a physical layer signal or higher layer signal. Thenumber of times of repetition/unit size according to each resourceregion may be preset, or signaled to the UE by the network through aphysical layer signal or higher layer signal. This configuration mayensure the operation of smooth multiplexing of UEs which have differentnumbers of times of repetition/unit sizes and prevent unnecessary blinddecoding in the receiving UE. If it is determined that a UE is out ofcoverage, the UE may transmit the D2D signal at a predetermined transmitpower in a predetermined resource region a predetermined number of timesof repetition.

Differently setting the transmit power and/or the number of times ofrepetition for each resource pool may be configured each step of atarget range. For example, if a discovery range of 3 steps(short/medium/long) is configured, the resource region may be dividedinto 3 regions, and different transmit powers and/or numbers of times ofrepetition may be set for the respective regions to distinguish betweenthe ranges. Each UE selects a resource according to a target range of anapplication or service, and transmits a D2D signal at the transmitpower/the number of times of repetition set for the resource. For D2Dcommunication, the number of times of repetition in each resource poolmay be predetermined according to a target range or configured through ahigher layer signal, and a D2D signal transmitting UE may transmit a D2Dcommunication packet by setting the number of times of repetition andtransmit power according to the target range. To simplify multiplexingbetween the UEs having different numbers of times of repetition, thetransmission resource pools may be distinguished from each otheraccording to the numbers of times of repetition. Similar to discovery,the transmit power and the number of times of repetition for each D2Dresource pool may be predetermined or signaled through a higher layersignal. Herein, the number of times of repetition may be the maximum,minimum or average number of times of repetition in the correspondingresource pool. Similar to D2D communication, the transmit power and/orthe number of times of repetition may be predetermined according to thescheduling assignment (SA) pool or target range, or signaled to the UEthrough a physical layer signal or higher layer signal.

Determination of the Number of Times of Repetition According to theSignal Strength from the eNB

The number of times of repetition of transmission of a discovery signalmay be determined according to the signal strength (RSRP, etc.) from theeNB. Herein, the number of times of repetition may refer to the numberof times of repetition within one period of a discovery resource or themaximum possible number of times of transmission within a predeterminedtime. For example, the number of times of repetition of transmission ofa discovery signal may be set to M if the RSRP is greater than or equalto a threshold, and set to N if the RSRP is less than the threshold.Herein, as the RSRP increases (namely, the distance from the eNBdecreases), the set transmit power of a discovery signal decreases.Accordingly, M may be set to be greater than N to compensate for loss ofcoverage according to the transmit power through repetition oftransmission. More generally speaking, the number of times of repetitionof transmission of a discovery signal may be preset according to theRSRP as shown in Table 1 below.

TABLE 1 Repetition number RSRP (R) of discovery signal R < P1 M1 P1 < R< P2 M2 . . . . . . PT-1 < R < PT MT

The number of times of repetition according to the signal strength (ortransmit power) of the eNB may be pre-configured or delivered by thenetwork through physical layer signaling (such as SIB and PDCCH/EPDCCH)or higher layer signaling (RRC signaling). For a UE which is out ofcoverage, the network operator may operate according to a preset value.If configurations as shown in Table 1 are signaled to the UE, thethreshold value for each boundary and the number of times of repetitionfor each region may be carried by a physical layer signal or higherlayer signal.

The configurations described above may address an issue (difference inperformance between a UE at a cell boundary and a UE at the center of acell) which may be raised in performing open loop power control toprotect PUCCH transmission.

Configuring a Discovery Unit According to the Signal Strength from theeNB

The aforementioned operation of setting the number of times ofrepetition according to the strength of a signal of the eNB may also beimplemented by increasing (or decreasing) the size of a discovery signalunit. That is, the size of a discovery unit may be set according to thesignal strength from the eNB. For example, if the signal strength of theeNB is greater than or equal to P, 2 RBs×2 SFs may be set as onediscovery signal unit. If the signal strength of the eNB is less than P,2RBs×1 SF may be set as one discovery signal unit. The size of onediscovery signal unit may be determined with the number of SFs in thetime domain and the number of RBs in the frequency domain. The discoverysignal unit size according to the RSRP may be pre-configured, or bedelivered by the network through physical layer signaling (such as SIBand PDCCH/EPDCCH) or higher layer signaling (RRC signaling). For a UEwhich is out of coverage, the network operator may operate according toa preset value.

The number of times of repetition (or unit size) in a resource pool maybe determined by the frequency (and/or time) resources size of theresource pool or the system bandwidth. For example, if the number ofsystem bandwidth is greater than or equal to a certain number of RBs,the number of times of repetition (or unit size) may be set to A. If thenumber of system bandwidth is less than the certain number of RBs, thenumber of times of repetition (or unit size) may be set to B. Thismethod is intended to multiplex D2D signals of more UEs or lowerinterference according to repetition by reducing the number of times ofrepetition in the first place because sufficient frequency (and/or time)diversity cannot be obtained if the frequency resource size is small. Onthe other hand, if the resource pool size or system bandwidth is greaterthan or equal to a certain threshold, more repetitions may be allowed tosecure a wider D2D range because it is expected that there will besufficient resources and collision is less likely to occur. Togeneralize, the number of times of repetition (unit size) according tothe resource pool size (or system bandwidth) may be predetermined as astep. For example, the frequency size (or the system bandwidth size) ofa D2D resource pool may be divided into N steps, and the number of timesof repetition (or unit size) for each step may be predetermined. Asanother method, the number of times of repetition may be determinedaccording to the unit size (PRB size) or information bit size of the D2Dsignal. For example, the number of times of repetition may be set to aif the unit size is A PRB pairs, and may be set to b if the unit size isB PRB pairs. As another example, the number of times of repetition maybe set to c if the information bit size is greater than or equal to acertain size, and may be set to d if the information bit size is lessthan the certain size. This method is intended to secure a certaincoding rate or obtain an energy gain by increasing the number of timesof repetition when the unit size of the D2D signal is set to be small.If the unit size is set to be greater than or equal to a certain size,repetition may not be set or the number of times of repetition may bereduced to prevent the resources from being unnecessarily wasted becausea sufficient coding gain can be obtained. In the case where the unitsize of the D2D signal is fixed, if the information bit size isexcessively large, sufficient D2D coverage cannot be secured because asufficient coding rate cannot be secured. In this case, the number oftimes of repetition may be increased to obtain an energy gain or reducean effective coding rate. The number of times of repetition (or unitsize) according to the resource size (or system bandwidth), D2D signalunit size or information bit size may be set for scheduling assignment(SA), type 1 discovery, and type 2 discovery, separately, and somenumbers of times of repetition may be set to values signaled by thenetwork. For example, when it is assumed that type 1 discovery and type2 discovery operate only within the network, the numbers of times ofrepetition (or unit sizes) for the respective resource pools for the twoD2D signals may not be predetermined, but may always be set to valuesconfigured by the network. However, for SA, if a UE which is out ofcoverage transmits a D2D communication packet, a preset number of timesof repetition (or unit size) may be needed. In this case, the number oftimes of repetition (or unit size) which is preset by the systembandwidth may be used. The preset number of times of repetition (or unitsize) may be predetermined according to the size of the resource pool(or system bandwidth), and if the network indicates the number of timesof repetition (or unit size) through a higher layer signal, operationmay be performed according to the indicated number of times ofrepetition (or unit size). Alternatively, if the number of times ofrepetition is indicated by another UE through a PD2DSCH or a D2D signalof a higher layer (or a physical layer other than the PD2DSCH) in apartial network coverage, a rule may be defined such that the indicatednumber of times of repetition (or unit size) is used.

The configurations described above may address an issue (difference inperformance between a UE at a cell boundary and a UE at the center of acell) which may be raised in performing open loop power control toprotect PUCCH transmission.

Restriction on the Frequency Resource Region

As another method to lower interference applied to PUCCH transmission indiscovery signal transmission, the frequency resource region may berestricted. If a UE close to the eNB transmits a discovery signal usinga resource near a PUCCH resource, severe interference may be applied tothe PUCCH region due to inband emission (particularly, EVM-shoulderdetermined according to the EVM requirement) of the signal. Referring toFIG. 7, if the region indicated by a circle overlaps the PUCCH region(the region next to the region for a useful signal overlaps the PUCCHresources), severe interference may be applied to the PUCCH.Accordingly, the resource region for the discovery signal may berestricted in the frequency domain to prevent resources around the PUCCHresources from being used for D2D discovery signal transmission.Restriction on transmission in the frequency resource region (oravailable frequency region) may be selectively applied according to thesignal strength (RSRP or RSRQ) of the eNB, and the threshold value ofthe signal strength of the eNB and the restricted transmission region(or available frequency region) which are necessary for the selectedapplication may be pre-indicated to the UE through a higher layer signal(e.g., RRC) or physical layer signal (e.g., (E)PDCCH or SIB).

As a specific example, referring to FIG. 6, UEs (of UE group #1) havingRSRP greater than or equal to a predetermined value may be restrictednot to use resource pool 2. This operation may be understood as definingthe mapping relationship between the resource pools and RSRP in theprevious embodiment in which resource pools are respectively configuredfor each RSRP. That is, the resource pools may be configured forrespective RSRPs in a manner that as the RSRP increases, thecorresponding resource pool moves away from the PUCCH region. That is,in FIG. 6, the available resource regions for UE group #1 and UE group#2 are configured to be separated from each other in the frequencydomain. The available resource region according to the received signalstrength (RSRP or RSRQ) from the eNB may be pre-configured or beindicated to the UE through a higher layer signal (e.g., RRC signal) orphysical layer signal (e.g., (E)PDCCH or SIB).

The aforementioned method of distinguishing between the frequencyresource regions according to the signal strengths from the eNB may alsobe implemented by distinguishing between the frequency resourcesaccording to the transmit powers of UEs. For example, a UE having atransmit power greater than or equal to a dBm (or having the maximumtransmit power of X dBm) may transmit a D2D signal in the resourceregion for UE group #1 of FIG. 6, and a UE having a transmit power lessthan or equal to a dBm (or having the maximum transmit power of Y dBm)may use the resource region for UE group #2. To implement thisoperation, the transmit power, the range of transmit power or therepresentative value of transmit power for indicating the range oftransmit power may be predefined or signaled to the UE through aphysical layer signal or a highly signal for each resource region.

Separation of the frequency regions described above may also beimplemented by changing the transmission probability rather than byexplicitly distinguishing between the resource regions. For example, theUE having a received signal strength from the eNB which is greater thanor equal to a threshold may set the transmission probability of adiscovery signal by reducing the average value or preset value by acertain offset (>0) in areas near the PUCCH region. By setting differenttransmission probabilities for the respective frequency regions toprotect the PUCCH resources, a UE near the eNB may be almost preventedfrom performing signal transmission on RBs near the PUCCH resources. Thetransmission probabilities for RBs in the frequency domain may be afunction of received signal strengths of the eNB. The transmissionprobability on an RB near the PUCCH resources may be changed in inverseproportion to the strength of the received signal of the eNB. Thisadjustment of transmission probabilities for respective RBs in thefrequency domain may also be implemented by applying an offset withrespect to an average transmission probability. In this case, the offsetvalue may be set to increase on an RB near the PUCCH resource as thesignal strength of the eNB decreases, and to decrease on an RB near thePUCCH resource as the signal strength of the eNB increases. As anotherexample, a specific offset for the transmission probabilities may beconfigured for (pre-configured for or signaled, through a higher layersignal such as an RRC signal, to) the UE, and whether or not to use theoffset may be determined according to the received signal strength fromthe eNB.

Setting Different Transmit Powers for Frequency Positions

As an example configured by loosening the restriction on the frequencyresource region, the discovery transmit power may be restricted whileuse of resources near the PUCCH resource are allowed even if the RSRP isgreater than or equal to a threshold value. That is, in FIG. 6, UEs ofUE group #1 are allowed to select resource for 2, and transmit power isrestricted if a discovery signal is transmitted in resource pool 2. Inthis case, the maximum transmit power may be restricted, or the minimumtransmit power P_(0_D2D_Discovery) may be set differently for therespective frequency resources. For example, UEs of UE group #2 of FIG.6 may be configured to perform transmission at a power less than orequal to a threshold on the resources near the PUCCH resource region, orP_(0_D2D_Discovery) may be set to have a lower value near the PUCCHregion than in the other regions. The maximum transmit power for eachfrequency region may be defined as a function of the received signalstrength from the eNB. For example, the maximum transmit power onresources near the PUCCH region may be set to change in inverseproportion to the received signal strength from the eNB.

PUCCH Power Control

The descriptions given above relate to methods for imposing restrictionson a discovery signal (e.g., selection of a resource pool, determinationof a frequency region, transmit power control) in terms of therelationship between discovery signal transmission and PUCCHtransmission. In contrast, alleviation of interference may be achievedin terms of PUCCH power control. That is, PUCCH power control may be setto be different from power control in a subframe which has no relationto discovery signal transmission in a region in which a discovery signalis expected to be transmitted. In other words, a transmit power used forPUCCH transmission in a subframe in which a discovery signal istransmitted may be set to be greater than a transmit power used forPUCCH transmission in a subframe in which the discovery signal is nottransmitted.

Specifically, PUCCH power control according to an embodiment may beimplemented by Equation 5.

$\begin{matrix}{{P_{PUCCH}(i)} = {\min{\begin{Bmatrix}{{{P_{{CMAX},c}(i)},}\mspace{680mu}} \\{P_{0_{—}{PUCCH}} + {PL}_{c} + {h\left( {n_{CQI},n_{HARQ},n_{SR}} \right)} + {\Delta_{F_{—}{PUCCH}}(F)} + {\Delta_{TxD}\left( F^{\prime} \right)} + {g(i)}}\end{Bmatrix}\mspace{11mu}\lbrack{dBm}\rbrack}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

P_(O_PUCCH) is set to a value indicated by a higher layer. In thisembodiment, separate P_(O_PUCCH) may be indicated through a higher layersignal (e.g., RRC signal) such that a different transmit power is usedin a subframe (SF) in which a discovery signal is transmitted. Herein,P_(O_PUCCH) may be divided into P_(UE_PUCCH) and P_(O_NOMINAL_PUCCH),and only P_(UE_PUCCH) may be indicated through separate higher layersignaling (e.g., RRC signaling) to boost power only for UEs transmittingPUCCHs in an SF in which the discovery signal is transmitted. As anothermethod, a predetermined offset may be applied to P_(UE_PUCCH), andindicated through a higher layer signal. In the equation above, theother variables are already described in the section related to UL powercontrol, and thus other description thereof will be omitted.

By boosting the PUCCH transmit power, uniqueness of transmission of adiscovery signal may be reflected. More specifically, if a UE in the RRCidle mode can transmit a discovery signal, a UE to transmit a discoverysignal transmits the signal at timing different from the existingtransmission timing for the uplink signal as it is not aware of timingadvance (TA). This may cause the eNB to lose orthogonality with theuplink signal. Thereby, high interference is likely to be observed dueto ICI in the subframe in which the discovery signal is transmitted. Inthis case, stable PUCCH transmission may be implemented by boosting thePUCCH transmit power.

SRS Power Control

In the same context, power of the SRS may also be boosted in an SF inwhich the discovery signal is transmitted, compared to the conventionaloperation. If an SRS is transmitted in an SF in which the discoverysignal is transmitted higher interference may be applied than in otherSFs, and accordingly the network may instruct the SRS to be transmittedat a higher power in the SF. The existing SRS power control is given byEquation 6.P _(SRS,c)(i)=min {P _(CMAX,c)(i),P _(SRS_OFFSET,c)(m)+10 log₁₀(M_(SRS,c))+P _(O_PUSCH,c)(j)+α_(c)(j)·PL _(c) +f _(c)(i)}[dBm]  Equation6

P_(O_PUSCH,c) and α_(c) have values indicated by a higher layer. If anSRS is transmitted in an SF in which the discovery signal istransmitted, a value different from the value given in SFs in which thediscovery signal is not transmitted may be indicated by the network.This value may be indicated to the UE through higher layer signaling(e.g., RRC signaling). Herein, P_(O_PUSCH,c) may be divided intoP_(UE_PUCCH, c) and P_(O_NOMINAL_PUCCH,C) and indicated. To apply SRSpower boosting only to the UE that transmits an SRS in an SF in whichthe discovery signal is transmitted, only P_(UE_PUCCH, c) may besignaled to the UE through a separate higher layer signal. In addition,if an SRS is transmitted in an SF in which the discovery signal istransmitted, P_(SRS_OFFSET, c) may be indicated through separate higherlayer signaling (e.g., RRC signaling).

If the discovery signal is hardly transmitted, the PUCCH and SRS powercontrol described above, which is performed to additionally apply atransmit power on the assumption that the discovery signal istransmitted, may become unnecessary or severely degrade the receptionquality of the discovery signal due to power boosting of the PUCCH andSRS. To address this issue, PUCCH and/or SRS power boosting may beoptionally employed only when the discovery signal greater than or equalto a certain threshold value is observed. For example, a UE to transmita PUCCH or SRS may be pre-configured to observe a discovery signal in acertain window (e.g., performs energy sensing in a region in which thediscovery signal is transmitted (or in the PUSCH region) beforetransmitting the PUCCH or SRS and to optionally perform power boostingonly when the signal or receive power which is greater than or equal toa certain threshold is observed.

A combination of one or more of the methods for lowering interferencebetween the D2D signal (e.g., discovery signal) and the PUCCH signaldescribed above may be used. For example, the eNB may select a discoveryresource pool according to the signal strength, and the transmit powerfor PUCCH transmission in an SF in which the discovery signal istransmitted may be set to be greater than the transmit power in an SF inwhich the discovery signal is not transmitted. As another example, amethod for identifying power control and resources (configuration ofresource pools for respective RSRPs, restriction on the frequencyresource region, or the like) according to the signal strength of theeNB may be used as well.

The aforementioned method may be selectively used according to whetheror not a CP length is configured. If the same CP is configured for acellular signal and a discovery signal, influence of the inband emissionis considered. However, if different CPs are configured for the cellularsignal and discovery signal, not only the inband emission but also ICIaccording to loss of orthogonality should be considered. Accordingly, ifthe wide-area network (WAN) signal (e.g., cellular signal) and thediscovery signal have the same CP length, only the restriction on theavailable frequency region is employed. If different CP lengths areused, however, PUCCH power control and SRS power control may be employedin addition to the restriction on the available frequency region.

The proposed methods are not limited to transmission of a discoverysignal. Some of the proposed methods may be selectively used when a D2Dcommunication signal, a scheduling allocation signal for communicationor a D2D synchronization signal is transmitted. Herein, schedulingallocation refers to a control signal including a transmission resourceposition and ID of a D2D communication packet prior to transmission ofthe D2D communication packet. In addition, for the power control, whendifferent D2D transmission signal are given, the same power controlparameter may be used, or different parameters (e.g., P0, alpha, poweroffset, and the like) may be separately configured/signaled for therespective signals.

For example, closed-loop power control may be used for transmission of aD2D communication signal in an operation mode operated under control ofthe eNB, and some of the proposed methods may be used in a mode operatedin a situation where D2D communication signals are not individuallycontrolled by the eNB.

Configuration of Apparatuses According to an Embodiment of the PresentInvention

FIG. 8 is a diagram illustrating configurations of a transmission pointand a UE according to an embodiment of the present invention.

Referring to FIG. 8, a transmission point 10 may include a receptionmodule 11, a transmission module 12, a processor 13, a memory 14, and aplurality of antennas 15. The antennas 15 represent a transmission pointthat supports MIMO transmission and reception. The reception module 11may receive various signals, data and information from a UE on uplink.The transmission module 12 may transmit various signals, data andinformation to a UE on downlink. The processor 13 may control overalloperation of the transmission point 10.

The processor 13 of the transmission point 10 according to oneembodiment of the present invention may perform operations necessary forthe embodiments described above.

Additionally, the processor 13 of the transmission point 10 may functionto operationally process information received by the transmission point10 or information to be transmitted to the outside, etc. The memory 14,which may be replaced with an element such as a buffer (not shown), maystore the processed information for a predetermined time.

Referring to FIG. 8, a UE 20 may include a reception module 21, atransmission module 22, a processor 23, a memory 24, and a plurality ofantennas 25. The antennas 25 mean that the UE supports MIMO transmissionand reception. The reception module 21 may receive various signals, dataand information from an eNB on downlink. The transmission module 22 maytransmit various signals, data and information to the eNB on uplink. Theprocessor 23 may control overall operation of the UE 20.

The processor 23 of the UE 20 according to one embodiment of the presentinvention may perform operations necessary for the embodiments describedabove.

Additionally, the processor 23 may function to operationally processinformation received by the UE 20 or information to be transmitted tothe outside, and the memory 24, which may be replaced with an elementsuch as a buffer (not shown), may store the processed information for apredetermined time.

The configurations of the transmission point and the UE as describedabove may be implemented such that the above-described embodiments areindependently applied or two or more thereof are simultaneously applied,and redundant description of parts described above is omitted forclarity.

Description of the transmission point 10 in FIG. 8 may also be appliedto a relay which serves as a downlink transmitter or an uplink receiver,and description of the UE 20 may be applied to a relay which serves as adownlink receiver or an uplink transmitter.

The embodiments of the present invention may be implemented throughvarious means such as, for example, hardware, firmware, software, or acombination thereof.

When implemented by hardware, a method according to embodiments of thepresent invention may be embodied as one or more application specificintegrated circuits (ASICs), one or more digital signal processors(DSPs), one or more digital signal processing devices (DSPDs), one ormore programmable logic devices (PLDs), one or more field programmablegate arrays (FPGAs), a processor, a controller, a microcontroller, amicroprocessor, etc.

When implemented by firmware or software, a method according toembodiments of the present invention may be embodied as a module, aprocedure, or a function that performs the functions or operationsdescribed above. Software code may be stored in a memory unit andexecuted by a processor. The memory unit is located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

Preferred embodiments of the present invention have been described indetail above to allow those skilled in the art to implement and practicethe present invention. Although the preferred embodiments of the presentinvention have been described above, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention. For example, those skilled in the art may use a combinationof elements set forth in the above-described embodiments. Thus, thepresent invention is not intended to be limited to the embodimentsdescribed herein, but is intended to have the widest scope correspondingto the principles and novel features disclosed herein.

The present invention may be carried out in other specific ways thanthose set forth herein without departing from the spirit and essentialcharacteristics of the present invention. Therefore, the aboveembodiments should be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. The present invention is not intendedto be limited to the embodiments described herein, but is intended tohave the widest scope consistent with the principles and novel featuresdisclosed herein. In addition, claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention as described above areapplicable to various mobile communication systems.

The invention claimed is:
 1. A method for transmitting a discoverysignal by a Device-to-Device (D2D) terminal in a wireless communicationsystem, the method comprising: selecting, by the D2D terminal, aresource pool from among resource pools configured by a networkaccording to a Reference Signal Received Power (RSRP) measurement resultfor a signal of the network at the D2D terminal, wherein a RSRP rangeconfigured for the resource pools is signaled through a Radio ResourceControl (RRC) signaling from the network; determining, by the D2Dterminal, resources to repeatedly transmit a discovery signal within theselected resource pool by applying a hopping pattern; and repeatedlytransmitting, by the D2D terminal, the discovery signal using thedetermined resources.
 2. The method according to claim 1, wherein openloop power control is applied to the transmitting of the discoverysignal.
 3. The method according to claim 1, wherein a size of a resourceunit for transmitting the discovery signal varies according to the RSRPmeasurement result.
 4. The method according to claim 3, wherein, whenthe D2D terminal is an out-of-coverage terminal, the size of theresource unit for transmitting the discovery signal is preset by anetwork operator.
 5. The method according to claim 1, wherein a givennumber of times of repetition of the discovery signal is allocated toeach of the resource pools.
 6. The method according to claim 5, whereinthe number of times of repetition is determined according to a size ofthe resource pool in a frequency domain.
 7. The method according toclaim 1, wherein a transmit power used in transmitting a physical uplinkcontrol channel in a subframe used to transmit the discovery signal isgreater than a transmit power used in transmitting the physical uplinkcontrol channel in a subframe unused to transmit the discovery signal.8. The method according to claim 7, wherein a parameter related to thetransmit power used in transmitting the physical uplink control channelin the subframe used to transmit the discovery signal is deliveredthrough higher layer signaling.
 9. A Device-to-Device (D2D) terminal fortransmitting a discovery signal in a wireless communication system, theD2D terminal comprising: a transceiver; and a processor, wherein theprocessor is configured to: select a resource pool from among resourcepools configured by a network according to a Reference Signal ReceivedPower (RSRP) measurement result for a signal of the network at the D2Dterminal, wherein a RSRP range configured for the resource pools issignaled through a Radio Resource Control (RRC) signaling from thenetwork; determine resources to repeatedly transmit a discovery signalwithin the selected resource pool by applying a hopping pattern; andcontrol the transceiver to repeatedly transmit the discovery signalusing the determined resources.